Molding metal mold and method for producing the molding metal mold

ABSTRACT

The present invention aims to provide a molding metal mold capable of increasing the supporting rigidity of an insert. A molding metal mold is provided for forming a cavity between a first metal mold and a second metal mold and for molding a product the cavity, wherein the first metal mold includes: an insert having a part of a cavity surface on one end side; a body member for externally holding the insert; and a plurality of spherical bodies interposed between the insert and the body member and performing alignment of the insert, the plurality of spherical bodies being closely filled between the insert and the body member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a molding metal mold and a method for producing the molding metal mold.

2. Description of the Related Art

A lens frame as a member for supporting an optical system such as a digital camera and a telephoto lens has a great influence on the precision of an optical axis of the optical system, and therefore needs to have a high processing accuracy. Because the accuracy of the optical axis is especially important for performance and quality of a product, in case the optical system uses ten lenses, for example, usually the lens frame is pre-manufactured such that one of the lenses can be fine-adjusted to make a final adjustment of the optical axis. Recently, a small lens frame produced by means of plastic molding is widely used as a lens frame for supporting an optical system of, for example, a film camera having a lens and a portable phone equipped with a camera. Further, the lens making up the optical system itself is formed by means of plastic injection molding. Also in the production of such a lens, the accuracy of the optical axis is vitally important.

As a molding metal mold capable of accurately producing a product, a molding metal mold 500 is known having a first metal mold 600 and a second metal mold 700 with a cavity formed therebetween in which a product is injection molded, as shown in FIG. 3. See Japanese Patent Application Laid-Open (Kokai) No. 2003-231159 (FIG. 1), for example. The first metal mold 600 comprises: an insert 610 having a cavity surface 610 a; a body member 620 for externally holding the insert 610 and having a convex taper 621 on an end surface on the side of the second metal mold 700; and ball bearings 630 interposed between the insert 610 and the body member 620. The second metal mold 700 comprises: an insert 710 having a cavity surface 710 a; a body member 720 for externally holding the insert 710 and having a concave taper 721 on an end surface on the side of the first metal mold 600; and ball bearings 730 interposed between the insert 710 and the body member 720.

In such a metal mold, alignment between the insert 610 and the body member 620 and between the insert 710 and the body member 720 is performed with the ball bearings 630, 730 interposed therebetween, and alignment between the first metal mold 600 and the second metal mold 700 is conducted by means of the convex taper 621 and the concave taper 721.

The conventional molding metal mold 500 is constructed to remove the product from the cavity by moving the insert 610 when the mold is opened. Thus, in the conventional molding metal mold 500, in order to prevent adjacent spherical bodies from being ground to each other and abraded when the insert 610 moves, the ball bearings 630, 730 each comprise a plurality of spherical bodies and a retainer case that maintains the spherical bodies separated from each other.

However, in such a conventional molding metal mold 500, the number of spherical bodies that can be provided is limited because the retainer case is interposed between the spherical bodies. The larger the number of the spherical bodies supporting the inserts 610, 710, the greater supporting rigidity the inserts 610, 710 has with respect to the body members 620, 720. However, the conventional molding metal mold 500, because it has the retainer case, was incapable of increasing the supporting rigidity of the inserts 610 than a certain level. Small supporting rigidity of the inserts 610 would cause movement of the insert 610 during injection molding, thus resulting in a problem of disallowing an accurate production of a product.

Also, the conventional molding metal mold 500 has a clearance S for the insert 610 to move in when the mold is clamped, because the molding metal mold 500 is designed to remove the product from the cavity by pushing out the insert 610 from the body member 620 when the mold is opened. This increases the distance from the cavity surface 610 a of the insert 610 to a supporting point (a spherical body of one tip end of the ballbearings) of the insert 610, causing a problem of reduced supporting rigidity (increased deflection amount) of the insert 610 and thus reduced product accuracy.

Further, in the conventional molding metal mold 500, the number of providable spherical bodies is limited by the retainer case interposed between the spherical bodies, which also restricts heat transmission path between the insert 610 and the body member 620. This hampers a sufficient control of temperature increase of the insert due to melted resin, causing a problem of lengthened growth cycle.

In light of such a problem, this invention aims to provide a molding metal mold capable of increasing supporting rigidity and heat transmissibility of the insert, and a method for producing the molding metal mold.

SUMMARY OF THE INVENTION

The molding metal mold according to the present invention is one for forming a cavity between a first metal mold and a second metal mold and for molding a product the cavity, wherein the first metal mold comprises:

an insert having a part of a cavity surface on one end side;

a body member for externally holding the insert; and

a plurality of spherical bodies interposed between the insert and the body member and performing alignment of the insert, the plurality of spherical bodies being closely filled between the insert and the body member.

According to this construction, because the plurality of spherical bodies are closely filled between the insert and the body member, the supporting rigidity of the insert can be increased compared to a conventional molding metal mold having a retainer case.

Further, according to this construction, because the plurality of spherical bodies are closely filled between the insert and the body member, the heat transmission path is increased between the insert and the body member, thus allowing rapid control of the insert temperature.

Here, the status in which “the plurality of spherical bodies are closely filled between the insert and the body member” means, for example, a status in which the space between the insert and the body member is filled only by the plurality of spherical bodies, without a retainer case and a spacer.

Also, the second metal mold is not limited to a specific construction, but may comprise an insert and a body member as in the first metal mold, or comprise a single member without being separated.

At least one of the first and second metal molds preferably comprises an extrusion pin provided protrudably from the cavity surface.

According to this construction, it is not necessary to move the insert to remove the molded product, and therefore the spherical bodies are not ground to each other and abraded. Thus, omission of the retainer case and the space does not cause the spherical bodies to change in shape (diameter), which allows it to accurately locate the insert at a predetermined position. Also, because the insert and the body member are not fixed to each other unlike the case of “shrinkage fitting”, for example, it is easy to disintegrate the metal mold for maintenance.

Further, because it is not necessary to provide a clearance (S in FIG. 3) for the insert to move in, the distance between the cavity surface formed on one end side of the insert and the supporting point of the insert is reduced, thus increasing the supporting rigidity of the insert.

The plurality of spherical bodies are preferably filled between the insert and the body member, while being applied with preload.

According to this construction, the insert can be supported with a greater supporting force, thereby allowing further increase of the supporting rigidity of the insert. To provide the spherical body with preload, metal spherical bodies may be used having a diameter slightly larger than the clearance between the insert and the body member. In this manner, the spherical bodies are filled therebetween while any of the body member, insert, and spherical bodies is elastically deformed, with its resilience acting as the preload.

It is preferable that the insert comprises a column portion having the partial cavity surface; and the body member comprise: a small hole portion opening in one end portion of the body member and fitting with one end side of the column portion; a large hole portion opening in other end portion of the body member, linking with other end portion of the small hole portion, and freely fitting with other end portion of the column portion; and the plurality of spherical bodies be closely filled between an external circumference surface of the column portion and an internal circumference surface of the large hole portion.

According to this construction, because the plurality of spherical bodies are closely filled between the external circumference surface of the column portion and the internal circumference surface of the large hole portion, the supporting rigidity of the insert can be increased.

Also, one end side of the insert is fitted in the small hole portion and other end side of the insert is freely fitted to the large hole portion of the body member. This prevents that the spherical bodies fall off therefrom, and that a molding material to be filled in the cavity enters the space between the other end side of the insert and the large hole portion while a product is being molded.

It is to be noted that the shape of the cross-section of the column portion is not limited to a specific one, but may be a cylinder or a prism, for example.

The above-mentioned molding metal mold is preferably produced by means of a method including: heating and thermally expanding the body member; and then filling the plurality of spherical bodies between the body member and the insert.

According to this method, the body member is heated and expanded, before the spherical bodies are closely filled between the body member and the insert. Therefore, spherical bodies larger than the clearance between the body member and the insert can be easily filled therebetween. Then, the heated and expanded body member returns to a normal temperature to shrink, thus applying preload to the spherical bodies. This can further increase the supporting rigidity of the insert.

According to the present invention, because a plurality of spherical bodies are closely filled between the insert and the body member, supporting rigidity of the insert can be increased, thereby allowing highly accurate molding of a product.

Further, according to the present invention, because a plurality of spherical bodies are closely filled between the insert and the body member, there exist more heat paths between the body member and the insert than when the retainer is interposed between the spherical bodies. As a result, more accurate control of the insert temperature becomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross sectional view of a molding metal mold according to the present embodiment, wherein the mold is clamped.

FIG. 1B is a cross sectional view of a molding metal mold according to the present embodiment, wherein the mold is opened.

FIG. 2A is a cross sectional view showing a step for filling spherical bodies between an insert and a body member.

FIG. 2B is a cross sectional view showing a step for filling spherical bodies between an insert and a body member.

FIG. 2C is a cross sectional view showing a step for filling spherical bodies between an insert and a body member.

FIG. 2D is a cross sectional view showing a step for filling spherical bodies between an insert and a body member.

FIG. 3 is a cross sectional view of a conventional molding metal mold.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, the best mode for carrying out the invention will be described in detail. In the description, the same elements are attached with the same numbers and a redundant description will be omitted. The present embodiment will describe a case in which the invention is applied to produce a lens mirror.

First, a construction of a molding metal mold according to the present embodiment will be described.

Reference will be made to FIGS. 1A and 1B, which are cross sectional views of a molding metal mold according to the present embodiment, wherein the mold is clamped and opened, respectively.

As shown in FIG. 1A, the molding metal mold 1 has a first metal mold 100 and a second metal mold 200 with a cavity C formed therebetween, in which a lens frame K is formed as a product. As shown in FIG. 1B, the lens frame K is a member for holding a plurality of lenses (not shown) constructing an optical system, which comprises a diaphragm s. In the present embodiment, of the construction of the lens frame K, one end side (right side in FIG. 1B) of the diaphragm s is formed by a portion of the cavity C formed in the second metal mold 200, and other side (left side in FIG. 1B) of the diaphragm s is formed by a portion of the cavity C formed in the second metal mold 100. The molding metal mold 1 according to the present embodiment is a metal mold capable of accurately forming the lens frame K so that optical axes of lenses placed on both side of the diaphragms correspond to each other.

The first metal mold 100 comprises: an insert 110 having, at tip end thereof, a partial cavity surface (hereinafter referred to as “cavity surface Ca”); a body member 120 to which the insert 110 is to be fitted; and metal spherical bodies 130 interposed between the insert 110 and the body member 120, as shown in FIG. 1A.

The insert 110 is a metal member provided as a separate part from the body member 120 for sharply forming an edge of the lens frame K, and comprises: an insert body 111; and a column portion 112 having a circular cross section extending from the center of one end side of the insert body 111, as shown in FIG. 1B.

The insert body 111 is a portion to be attached to a template of an injection molding apparatus (not shown), for example, and has a diameter larger than a large hole portion 122 to be described later.

The column portion 112 is a portion to fit with the body member 120, which comprises in the present embodiment: a small diameter portion 114 of a cylindrical shape having, on one end side thereof, the cavity surface Ca; and a large diameter portion 115 continuous to other end side of the small diameter portion 114, having a larger diameter than the small diameter portion 114, as shown in FIG. 1B.

The body member 120 is a metal member for externally holding the insert 110, having a cylindrical shape with a hollow portion at the center, as shown in FIG. 1B. The hollow portion of the body member 120 comprises: a small hole portion 121 to which is fitted the small diameter portion 114 formed on one end side of the column portion 112 of the insert 110; and the large hole portion 122 freely fitting with the large diameter portion 115 of the insert 110. On an end surface on one end side of the body member 120, a convex taper portion 123 with a conical frustum shape is provided, capable of aligning with the second metal mold 200.

The small hole portion 121 is formed to be approximately the same as or slightly larger than the small diameter portion 114 of the insert 110. Specifically, the small hole portion 121 is preferably larger than the small diameter portion 114 by 10-30 μm in diameter (5-15 μm in radius), and more preferably by 10-20 μm in diameter (5-10 μm in radius). One end side of the small hole portion 121 is an aperture on the surface on one end side of the body member 120. When the small diameter portion 114 of the insert 110 is fitted into the small hole portion 121, the cavity surface Ca formed on one end side of the small diameter portion 114 is exposed on the one end surface of the body member 120. Further, on the one end side of the small hole portion 121, a cavity surface Cb is formed.

The large hole portion 122 is formed to have a size (caliber) such that a clearance same as or sightly smaller than the spherical bodies 130 in diameter is provided around the large diameter portion 115 when the large diameter portion 115 of the insert 110 is inserted to the large hole portion 122. Other end side of the large hole portion 122 is an aperture on an end surface on other end side of the body member 120, to which the column portion 112 of the insert 110 can be inserted. One end portion of the large hole portion 122 is linked to other end side of the small hole portion 121.

On the end surface on the one end side of the body member 120, an extrusion pin E is provided for extruding a molded product from the cavity C. The extrusion pin E comprises: two pins connected at respective other end side; and an elastic body for biasing the two pins toward the second metal mold 200. One of the pins abuts with other end side of the second metal mold when the mold is clamped, as shown in FIG. 1A. The other of the pins protrudes from the cavity surface when the mold is opened, as shown in FIG. 1B. The extrusion pin E is placed in a concave portion formed on the end surface on the one end side of the body member 120. The concave portion has an aperture into which two members are fitted each having a through hole for inserting one of the pins.

The spherical bodies 130 are metal spheres interposed between the body member 120 and the insert 110, for supporting and aligning the insert 110. The spherical bodies 130 are closely filled in the clearance between the large diameter portion 115 and the large hole portion 122. In other words, the clearance between the large diameter portion 115 and the large hole portion 122 is filled only with a plurality of spherical bodies. Accordingly, the insert 110 is supported by more supporting points than when a retainer case or a space exists between the spherical bodies, which increases the supporting rigidity of the insert 110 with respect to the body member 120.

The spherical bodies 130 each have a diameter approximately the same of slightly larger than the clearance between the large diameter portion 115 and the large hole portion 122. Specifically, the spherical bodies 130 each preferably have a diameter larger by 1 to 6 μm than the clearance. In this manner, the spherical bodies 130 are filled in the clearance between the large diameter portion 115 and the large hole portion 122, while being elastically pressed. As a result, resilience of the spherical bodies 130 acts as preload which more rigidly supports the insert 110. An external circumference surface of the large diameter portion 115 and an internal circumference surface of the large hole portion 122 also abut with the spherical body 130 to elastically deform, with the resultant resilience acting as preload.

Further, the spherical bodies filled closely and thus touching to each other prevents a movement thereof, and benefits in increasing the supporting rigidity.

The large diameter portion 115 of the insert 110 has a length approximately the same as the large hole portion 122 of the body member 120. Therefore, when the insert 110 is fitted into the body member 120, there does not exist a clearance between a surface on one end side of the large diameter portion 115 and a surface on one end side of the large hole portion 122. Accordingly, the spherical bodies can be filled up to the vicinity of the end surface on one end side of the large hole portion 122, thus further increasing the supporting rigidity of the insert 110.

The second metal mold 200 comprises: an insert 210 having, at tip end thereof, a partial cavity surface (hereinafter referred to as “cavity surface Cb”); and a body member 220 into which the insert 210 is fitted, as shown in FIG. 1A.

The insert 210 comprises: an insert body 211; and a column portion 212 having a circular cross section extending from other end side (the side of the first metal mold 100) of the insert body 211, as shown in FIG. 1B. The column portion 212 has a conical frustum shape (taper shape), tapering toward other end side (the side of the first metal mold 100). The column portion 212 has, on other end side thereof, a partial cavity surface (hereinafter referred to as “cavity surface Cc”). The insert 210 comprises a sprue SP and a gate G linking one end side of the insert body 211 and the cavity surface Cc.

The body member 220 is a member to which the column portion 212 of the insert 210 is fitted, for adjusting the positional relationship between the first metal mold 100 and the second metal mold 200. The body member 220 is shaped in an approximate cylindrical, and has a flange formed on the other end side. As shown in FIG. 1B, the body member 220 has a hollow portion including from one to other end sides: a large hole portion 222 into which a column portion 212 of the insert 210 is fitted; a small hole portion 221 loosely fitting into the cavity surface Cc formed on other end side of the column portion 212; and a concave taper portion 223 fitting with the convex taper portion 123 of the first metal mold 100. The large hole portion 222 is formed as a space with a taper shape tapering toward the other end side, and capable of aligning with the column portion 212 of the insert 210 fitted therein. The concave taper portion 223 is formed as a space with a taper shape tapering toward the one end side, and capable of aligning the first metal mold 100 and the second metal mold 100. The small hole portion 221 is smaller than the large hole portion 222 in diameter, and has an internal circumference surface on which a cavity surface Cd is formed.

Alignment of the molding metal mold 1 is carried out by fitting to each other the convex taper portion 123 of the first metal mold 100 and the concave taper portion 223 of the second metal mold 200, as shown in FIGS. 1A, 1B. Also, by combining the first metal mold 100 and the second metal mold 200, the cavity surfaces Ca, Cb, Cc, Cd are connected to each other to form the cavity C.

Next, a method will be discussed for closely filling the spherical bodies 130 between the insert 110 and the body member 120. FIGS. 2A to 2D are cross sectional views each showing a step for filling spherical bodies therebetween.

First, as shown in FIG. 2A, the column portion 112 of the insert 110 is inserted into the large hole portion 122 of the body member 120 so that one end side 115 a of the large diameter portion 115 and other end side 122 a of the large hole portion 122 are positioned at the same depth. Then, the spherical bodies 130 are placed in the clearance T formed between one end side of the large diameter portion 115 and other end side of the large hole portion 122. At this time, because the clearance T is slightly smaller than the diameter of the spherical bodies 130, the spherical bodies 13 do not enter the clearance T, being caught in the vicinity of the entrance of the clearance T.

Next, the column portion 112 of the insert 110 is pressed into the body member 120 by an amount corresponding to the diameter of the spherical bodies 130, as shown in FIG. 2B. At this time, by pressing one of the spherical bodies 130 to the one end side along with the insert 110, the spherical bodies 130 engage into the clearance T, rotating or sliding while elastically deforming, thus entering into the clearance T.

When the spherical bodies 130 have entered into the clearance T by the amount of the diameter thereof, subsequent spherical bodies 130 are placed in the vicinity of the entrance of the clearance T, as shown in FIG. 2C.

Then, by repeating several times the pressing of the column portion 112 (FIG. 2B) and the placement of the spherical bodies 130 (FIG. 2C), a plurality of spherical bodies 130 can be closely filled into the clearance T, as shown in FIG. 2D.

It is preferred that the spherical bodies 130 be filled to the bottom of the clearance T by means of a dedicated tool therefor. As such a dedicated tool, it is preferable to use one obtained, for example, by fitting two jigs, each having a semicircle shape, in the vicinity of other end side of the large diameter portion 115, to form a ring shape. This tool is moved to the one end side along the large diameter portion 115, so as to press the spherical bodies 130 into the clearance T.

As another filling method, the body member 120 may be heated to expand, before the spherical bodies 130 are filled into the clearance T. This increases the clearance T between the body member 120 and the insert 110 (large diameter portion 115), thereby facilitating it to fill into the clearance T the spherical bodies 130 larger than the clearance T in diameter, at a normal temperature. Also, as the temperatures of the body member 120, the insert 110 and the spherical bodies 130 become uniform, the spherical bodies 130 are applied with preload. That is, this method, can easily introduce the preload.

Further, if the clearance T is sufficiently larger than the diameter of the spherical bodies 130 when the body member 120 expands, then the spherical bodies 130 can be closely filled to (the bottom of) the one end side of the large hole portion 122 to the fullest. In this manner, the insert 110 is supported at a position close to the cavity surface Ca, thereby increasing the supporting rigidity of the insert 110.

Methods for heating the body member 120 includes, for example, pre-installing an electric heater in the body member 120, wrapping the body member 120 in an electric heating mat, using infrared radiation for non-contact heating, or housing the body member 120 in a thermostatic oven. The methods using the electric heater and the electric heating mat, which allow the filling operation while maintaining the body member 120 at a high temperature, are especially preferred.

Also, because the greater the temperature difference between the insert 110 and the body member 120, the larger the clearance T becomes, it is preferred to perform the filling operation while decreasing the temperature of the insert 110 as much as possible (without making the temperature high). Further, because the lower the temperature of the spherical bodies 130, the smaller the diameter thereof, it is preferred to carry out the filling operation while decreasing the temperature of the spherical bodies 130 as much as possible (without making the temperature high). The temperatures of the insert 110 and the spherical bodies 130 may be actively lowered by using a cool tank or coolant (e.g., cold water), for example.

Although the best mode for implementing the present invention has been described in detail with reference to the drawings heretofore, the invention is not limited thereto, but may be modified as needed within the scope and spirit of the present invention.

For example, although the present embodiment has discussed an example of applying the invention to a molding metal mold for producing the lens frame K, the invention is not limited thereto but may be applied to a metal mold for producing high precision parts such as a plastic optical lens.

Although, in the embodiment, the column portion 112 of the insert 110 comprises the small diameter portion 114 and the large diameter portion 115, no limitation is placed thereon, but the column portion 112 may have the same and constant thickness as the small hole portion 121 of the body member 120. In such a case, it is preferred to use spherical bodies having a diameter slightly larger than the difference between the radiuses of the large hole portion 122 and the small hole portion 121.

Although, in the embodiment, the spherical bodies 130 are filled in the clearance between the insert 110 and the body member 120 in an orderly manner, as shown in FIGS. 1A, 1B and FIGS. 2A to 2D, no limitation is placed thereon but the spherical body 130 may be filled in an unorderly manner.

No specific limitation is placed on the arrangement (method of placement) of the spherical bodies 130. For example, the spherical bodies 130 may be arranged in a rectangular lattice shape such that the centers of the spherical bodies 130 adjacent to each other in the direction of the axis of the metal mold are in parallel with the axis. Alternatively, the spherical bodies 130 may be arranged in a staggered shape such that the centers of the spherical bodies 130 adjacent to each other in the direction of the axis of the metal mold deviate in the direction of the circumference. The spherical bodies 130 can be filled more closely when arranged in the staggering shape than in the rectangular lattice shape. The clearance T preferably has a filling rate of not less than 20%, and more preferably of 50-65%. 

1. A molding metal mold for forming a cavity between a first metal mold and a second metal mold and for molding a product the cavity, wherein the first metal mold comprises: an insert having a part of a cavity surface on one end side; a body member for externally holding the insert; and a plurality of spherical bodies interposed between the insert and the body member and performing alignment of the insert, the plurality of spherical bodies being closely filled between the insert and the body member.
 2. A molding metal mold as claimed in claim 1, wherein the plurality of spherical bodies are filled between the insert and the body member, while being applied with preload.
 3. A molding metal mold as claimed in claim 1, wherein: the insert comprises a column portion having the partial cavity surface; the body member comprises: a small hole portion opening in one end portion of the body member and fitting with one end side of the column portion; a large hole portion opening in other end portion of the body member, linking with other end portion of the small hole portion, and freely fitting with other end portion of the column portion; and the plurality of spherical bodies are closely filled between an external circumference surface of the column portion and an internal circumference surface of the large hole portion.
 4. A molding metal mold as claimed in claim 3, wherein the plurality of spherical bodies are filled between the external circumference surface of the column portion and the internal circumference surface of the large hole portion, while being applied with preload.
 5. A molding metal mold as claimed in claim 1, wherein the second metal mold comprises: a second insert having a part of a cavity surface on one end side; a second body member for externally holding the insert; and a plurality of second spherical bodies interposed between the second insert and the second body member and performing alignment of the insert, the plurality of second spherical bodies being closely filled between the second insert and the second body member.
 6. A molding metal mold as claimed in claim 1, wherein at least one of the first and second metal molds comprises an extrusion pin provided protrudably from the cavity surface of the at least one of the first and second metal molds.
 7. A molding metal mold as claimed in claim 1, wherein: the insert comprises: a columnar small diameter portion having one end side and other end side, and having, on the one end side, the partial cavity surface; and a columnar large diameter portion coaxially connected to the other end side of the columnar small diameter portion; the body member comprises: a small hole portion having an aperture for exposing the cavity surface on the one end side of the columnar small diameter portion, and fitting with the columnar small diameter portion; and a large hole portion having an aperture which the other end side of the columnar small diameter portion can be inserted to and uninserted from, linking with the columnar small hole portion, and freely fitting with the columnar large diameter portion; when the molds are clamped, a surface extending between the columnar small diameter portion and the columnar large diameter portion abuts with a part of a surface extending between the small hole portion and the large hole portion; and the plurality of spherical bodies are closely filled between: an external circumference surface of the columnar large diameter portion; an internal circumference surface of the large hole portion; and a surface extending between the small and large hole portions, excluding a portion of a surface extending between the columnar small and large diameter portions.
 8. A molding metal mold as claimed in claim 7, wherein at least one of the first and second metal molds comprises an extrusion pin provided protrudably from the cavity surface of the at least one of the first and second metal molds.
 9. A molding metal mold as claimed in claim 7, wherein the plurality of spherical bodies are filled between the insert and the body member, while being applied with preload.
 10. A molding metal mold as claimed in claim 1, wherein the plurality of spherical bodies are made up of neighboring spherical bodies contacting to each other.
 11. A molding metal mold as claimed in claim 1, wherein the molding metal mold further comprises an electric heater built inside the body member, for heating and thermally expanding the body member when the filling of the plurality of spherical bodies is carried out.
 12. A molding metal mold as claimed in claim 1, wherein the molding metal mold further comprises an electric heating mat wrapped around the body member, for heating and thermally expanding the body member when the filling of the plurality of spherical bodies is carried out.
 13. A molding metal mold as claimed in claim 1, wherein the molding metal mold further comprises a temperature adjustment means for increasing the temperature of the body member before the filling of the plurality of spherical bodies is conducted, and decreasing the temperature of the body member after the filling of the plurality of spherical bodies is carried out.
 14. A molding metal mold as claimed in claim 1, wherein the molding metal mold further comprises a cooling means for cooling the insert during the filling of the plurality of spherical bodies.
 15. A molding metal mold as claimed in claim 1, wherein the molding metal mold further comprises a cooling means for cooling the insert before the filling of the plurality of spherical bodies is carried out.
 16. A molding metal mold as claimed in claim 1, wherein the plurality of spherical bodies is arranged in a rectangular lattice shape.
 17. A molding metal mold as claimed in claim 1, wherein the plurality of spherical bodies is arranged in a staggering shape.
 18. A molding metal mold as claimed in claim 1, wherein the closely filled plurality of spherical bodies has a filling rate not less than 20%.
 19. A molding metal mold as claimed in claim 1, wherein the closely filled plurality of spherical bodies has a filling rate of 50 to 60%.
 20. A method of producing a molding metal mold as claimed in claim 1, including heating and thermally expanding the body member; and then filling the plurality of spherical bodies between the body member and the insert. 